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…freeman dyson
x
16LONELY PLANET
大＿
it isn’t easy being an organism。 in the whole universe； as far as we yet know； there isonly one place； an inconspicuous outpost of the milky way called earth； that will sustain you；and even it can be pretty grudging。
from the bottom of the deepest ocean trench to the top of the highest mountain； the zonethat covers nearly the whole of known life； is only something over a dozen miles—not muchwhen set against the roominess of the cosmos at large。
for humans it is even worse because we happen to belong to the portion of living thingsthat took the rash but venturesome decision 400 million years ago to crawl out of the seas andbee land based and oxygen breathing。 in consequence； no less than 99。5 percent of theworld’s habitable space by volume； according to one estimate； is fundamentally—in practicalterms pletely—off…limits to us。
it isn’t simply that we can’t breathe in water； but that we couldn’t bear the pressures。
because water is about 1；300 times heavier than air； pressures rise swiftly as you descend—by the equivalent of one atmosphere for every ten meters （thirty…three feet） of depth。 on land；if you rose to the top of a five…hundred…foot eminence—cologne cathedral or the washingtonmonument； say—the change in pressure would be so slight as to be indiscernible。 at the samedepth underwater； however； your veins would collapse and your lungs would press to theapproximate dimensions of a coke can。 amazingly； people do voluntarily dive to such depths；without breathing apparatus； for the fun of it in a sport known as free diving。 apparently theexperience of having your internal organs rudely deformed is thought exhilarating （though notpresumably as exhilarating as having them return to their former dimensions uponresurfacing）。 to reach such depths； however； divers must be dragged down； and quite briskly；by weights。 without assistance； the deepest anyone has gone and lived to talk about itafterward was an italian named umberto pelizzari； who in 1992 dove to a depth of 236 feet；lingered for a nanosecond； and then shot back to the surface。 in terrestrial terms； 236 feet isjust slightly over the length of one new york city block。 so even in our most exuberantstunts we can hardly claim to be masters of the abyss。
other organisms do of course manage to deal with the pressures at depth； though quite howsome of them do so is a mystery。 the deepest point in the ocean is the mariana trench in thepacific。 there； some seven miles down； the pressures rise to over sixteen thousand pounds persquare inch。 we have managed once； briefly； to send humans to that depth in a sturdy divingvessel； yet it is home to colonies of amphipods； a type of crustacean similar to shrimp buttransparent； which survive without any protection at all。 most oceans are of course much shallower； but even at the average ocean depth of two and a half miles the pressure isequivalent to being squashed beneath a stack of fourteen loaded cement trucks。
nearly everyone； including the authors of some popular books on oceanography； assumesthat the human body would crumple under the immense pressures of the deep ocean。 in fact；this appears not to be the case。 because we are made largely of water ourselves； and water is“virtually inpressible；” in the words of frances ashcroft of oxford university； “the bodyremains at the same pressure as the surrounding water； and is not crushed at depth。” it is thegases inside your body； particularly in the lungs； that cause the trouble。 these do press；though at what point the pression bees fatal is not known。 until quite recently it wasthought that anyone diving to one hundred meters or so would die painfully as his or her lungsimploded or chest wall collapsed； but the free divers have repeatedly proved otherwise。 itappears； according to ashcroft； that “humans may be more like whales and dolphins than hadbeen expected。”
plenty else can go wrong； however。 in the days of diving suits—the sort that wereconnected to the surface by long hoses—divers sometimes experienced a dreadedphenomenon known as “the squeeze。” this occurred when the surface pumps failed； leadingto a catastrophic loss of pressure in the suit。 the air would leave the suit with such violencethat the hapless diver would be； all too literally； sucked up into the helmet and hosepipe。
when hauled to the surface； “all that is left in the suit are his bones and some rags of flesh；”
the biologist j。 b。 s。 haldane wrote in 1947； adding for the benefit of doubters； “this hashappened。”
（incidentally； the original diving helmet； designed in 1823 by an englishman namedcharles deane； was intended not for diving but for fire…fighting。 it was called a “smokehelmet；” but being made of metal it was hot and cumbersome and； as deane soon discovered；firefighters had no particular eagerness to enter burning structures in any form of attire； butmost especially not in something that heated up like a kettle and made them clumsy into thebargain。 in an attempt to save his investment； deane tried it underwater and found it was idealfor salvage work。）the real terror of the deep； however； is the bends—not so much because they areunpleasant； though of course they are； as because they are so much more likely。 the air webreathe is 80 percent nitrogen。 put the human body under pressure； and that nitrogen istransformed into tiny bubbles that migrate into the blood and tissues。 if the pressure ischanged too rapidly—as with a too…quick ascent by a diver—the bubbles trapped within thebody will begin to fizz in exactly the manner of a freshly opened bottle of champagne；clogging tiny blood vessels； depriving cells of oxygen； and causing pain so excruciating thatsufferers are prone to bend double in agony—hence “the bends。”
the bends have been an occupational hazard for sponge and pearl divers since timeimmemorial but didn’t attract much attention in the western world until the nineteenthcentury； and then it was among people who didn’t get wet at all （or at least not very wet andnot generally much above the ankles）。 they were caisson workers。 caissons were encloseddry chambers built on riverbeds to faci